In these days, a house is being developed which not only purchases electric power from a commercial electric power system, but also utilizes electric power generated by a photovoltaic panel, a small-sized aerogenerator, a fuel cell or the like provided in the house.
In a conventional home electric power system provided with the photovoltaic panel, electric power generated in the photovoltaic panel is converted to AC power by a power conditioner, and thereafter supplied to each domestic load or returned to the commercial electric power system via a distribution board that branches electric power from the commercial electric power system.
The conventional home electric power system will be described with reference to FIG. 6, for example.
In a home electric power system 101 shown in FIG. 6, electric power is supplied from an electric power network (electric power system) as the commercial electric power system to a distribution board 113 via a meter 112. Electric power supplied from the electric power system to the distribution board 113 is branched into breakers 123-1 to 123-6 via a safety breaker (SB) 121 and an earth leakage circuit breaker (ELB) 122, and supplied to each load such as a home electric appliance via a wall outlet, not shown, or the like.
Further, electric power generated in a photovoltaic panel 114, which is supplied to a power conditioner 116, is inputted into a DCAC (DC-AC) converting unit 132 via a PV (PhotoVoltanic) control unit 131, and is converted to AC power in the DCAC converting unit 132. An output-side terminal of the DCAC converting unit 132 is connected to a wire between the safety breaker 121 and the earth leakage circuit breaker 122 of the distribution board 113, and the electric power outputted from the DCAC converting unit 132 is supplied to the distribution board 113.
In such a home electric power system 101, the distribution board 113 and a power conditioner 116 are connected by a set of wires, and the electric power generated in the photovoltaic panel 114 is supplied to each domestic load and consumed, or returned to the electric power system and sold, via the distribution board 113.
Incidentally, with the aim of diffusion of photovoltaic power generation, there has been considered in each country the introduction of a system to purchase photovoltaically generated electric power at a higher price as compared with electric power other than that. In such an electric power trading system, electric power generated in the photovoltaic panel is allowed to be returned to the electric power system, but some of electric power from power sources other than the electric power generated in the photovoltaic panel is not allowed to be returned to the electric power system.
For this reason, there is, for example, proposed a power-conditioner control apparatus having a function to sense electric power generated in a gas cogeneration system and prevent the electric power from flowing out to the electric power system (e.g., Patent Document 1).